It is common in many surgical procedures to use surgical scissors for cutting tissue that is vascularized, i.e., contains blood vessels. The resultant bleeding that occurs is not only of concern from the standpoint of blood loss, but the blood may also obscure the surgical field or site. Controlling such bleeding has, in the past, required significant time and attention of the surgeon during many surgical procedures.
In recent years, efforts have been devoted to developing scissors that use radiofrequency ("RF") energy in a manner such that the tissue is heated as it is cut, to promote immediate hemostasis. Early efforts at such electrosurgial scissors used monopolar RF power, where the scissors constituted one electrode, and the patient rested on the other electrode, which was typically in the form of a conductive mat, to complete the circuit. Current flowed generally through the patient between the electrodes due to a voltage applied across the electrodes by an RF power supply.
Monopolar applications, however, had certain drawbacks. Inadvertent contact between the scissors and other tissue could result in unwanted tissue damage. In addition, the flow of current through the body of the patient could take uncertain or unpredictable paths with potential unwanted injury to other tissue. More recently, efforts have been made to develop bipolar electrosurgical scissors to overcome the drawbacks with monopolar scissors. Specifically, efforts have been made to develop scissors in which one blade includes one electrode and the other blade includes the other electrode, so that current flows between the blades as they cut the desired tissue.
Example of recent efforts to develop bipolar scissors are found in U.S. Pat. Nos. 5,324,289 and 5,330,471. These patents disclose bipolar scissors in which one blade of the scissors has one electrode, and the other blade of the scissors has the other electrode, so that current flows between the blades as they come into proximity during cutting. Various embodiments of bipolar scissors are disclosed in these patents, but typically a layer of insulating material is provided on at least one shearing surface of one of the blades, and the hinge pin or fastener which pivotally connects the blades is electrically insulated, so that the electrically active parts of the scissor blades do not contact each other during operation of the instrument. With the construction as shown in these patents, the electrical current flows between the blades at a point just forward of where the shearing surfaces actually touch. The current flow between the blades causes a heating of the tissue and promotes local coagulation and hemostasis during the cutting procedure.
In U.S. Pat. No. 5,352,222, bipolar scissors are shown in which each blade of the scissors is a laminated assembly of a metal shearing surface, a metal blade support and intermediate layer of insulating material. The blade support of one blade acts as one electrode, and the blade support of the other blade acts as the other electrode, so that electrical energy flows between the blade supports as the blades close on the tissue being cut. A short circuit between the shearing surface is prevented by reason of the insulating layer between the metal shearing surface and the blade support. This scissor construction is purported to be more economical to manufacture than the blade structure disclosed in U.S. Pat. Nos. 5,324,289 and 5,330,471. However, because the shearing surface is a separate piece, bonded to the blade support, a particularly high strength and high precision epoxy bonding process is required in the '222 patent so that the shearing surface remains attached to the blade support despite the shearing forces exerted upon it during repeated cutting.
What the above patents have in common, is that each blade forms one of the electrodes attached to a bipolar RF energy source, so that the only current that flows is between the blades as they close. Although the bipolar scissors described in the above-identified patents are believed to be an advance over the earlier monopolar scissors, they typically required the electrically active parts of the blades to be insulated from one another, which tends to complicate the design and materials of the blade actuating mechanism. Accordingly, development work continues to provide bipolar scissors which are easy to use, more economic to make, versatile and/or which are effective in promoting hemostasis during cutting of various tissues, particularly including tissues that are highly vascularized.